The present invention relates to a photomask, a manufacturing method thereof, a patterning method, and a semiconductor device manufacturing method, and particularly a technique effectively applied to the photolithography using ultraviolet radiation, far ultraviolet radiation, vacuum ultraviolet radiation, or the like as a light source.
To manufacture a semiconductor integrated circuit device (LSI: Large Scale Integrated circuit), a lithography technique is used as a method for forming a micropattern on a semiconductor wafer. In the case of the lithography technique, the so-called optical projective exposure method is mainly used which repeatedly transfers a pattern formed on a photomask onto, a semiconductor wafer through a reduction projection optics. A basic configuration of an exposure system is disclosed in Japanese Patent Laid-Open No. 2000-91192.
A resolution R on a semiconductor wafer in the projective exposure method is generally shown by R=kxλ/NA, where k denotes a constant depending on a resist material or a process, λ denotes a wavelength of illumination light, NA denotes a numerical aperture of a projective exposure lens. As seen by the above relational equation, a projective exposure technique using a light source with a shorter wavelength is required as patterns are made more fine. At present, an LSI is manufactured by a projective exposure system using g-line (λ=438 nm) or i-line (λ=365 nm) of a mercury lamp, or a KrF excimer laser beam (λ=248 nm) as a light source. For the purpose of achieving a finer pattern, it is studied to use an ArF excimer laser beam (λ=193 nm) or F2 excimer laser beam (λ=157 nm) having a shorter wavelength.
A normal photomask has a structure in which a thin film made of chromium or the like is formed as a shading film on a quartz glass transparent for exposure light. This photomask is manufactured by applying a resist onto a substrate in which a chromium film is attached to a quartz plate, exposing it in the form of a desired pattern prepared in advance, further developing it to form a resist pattern, and etching the chromium by using the resist pattern. In the case of this normal photomask, because steps of etching a chromium film and of peeling off the resist are required, it takes a lot of time to manufacture the photomask and the cost thereof increases.
Meanwhile, for example, Japanese Patent Laid-Open No. 5-289307 discloses a photomask using not chromium but a photoresist as a shading film. This is a mask using the fact that a photoresist has a shading characteristic relative to short wavelength rays such as ArF rays or the like. Because this technique makes it possible to fabricate a photomask without including a step of etching chromium, an effect of reducing the mask cost can be expected. Moreover, because there is no step of etching chromium, this technique has an advantage in that a pattern dimension accuracy can be ensured.